Process for electrolytic deposition of gold-copper-cadmium alloys



United States Patent 1 3,056,733 PROQESS FOR ELECTROLYTIC DEPOSITION 0F GOLD-COPPER-CADMIUM ALLOYS Gerhard Heilmann, Pforzheim, Germany, assignor to Deutsche Goldund Silber-Scheideanstalt vormals Roessler, Frankfurt am Main, Germany No Drawing. Filed Apr. 23, 1961, Ser. No. 106,182

Claims. (Cl. 204-44) The present invention relates to an improved process for the electrodeposit of bright coatings of gold-coppercadmium alloys.

In the electrolytic deposition of gold alloys baths are chiefly used which contain the gold and the alloying metals, such as silver, copper, cadmium, nickle and the like, in the form of cyanidic complex salts. Thicker deposits from such baths usually turn out to be more or less dull and lustreless. With suited bath composition and suited current density it is possible under favorable circumstances to produce more or less lustrous deposits but even in this case it is usually necessary to subject the coating deposited to a subsequent mechanical polishing in order to provide the lustre required, for example, in the jewelry and watch industry.

The use of periodically reversed direct current to improve the smoothness and lustre of electrolytic deposits, such as, for example, of gold, is generally known. However, the use of periodically reversed current, as is known in other electrolytic baths, in the galvanic deposition of gold alloys does not in itself provide advantages.

According to the invention it was unexpectedly found that, even when employing an anodic current density higher than the cathodic current density, highly lustrous gold-copper-cadium alloys can only be deposited provided certain bath compositions are maintained and in addition that a particular time sequence of anodic and cathodic connection is maintained. In the process according to the invention aqueous baths are employed at a pH of 9-11 and contain 1 to 3 g. per liter of gold as potassium gold cyanide 5 to g., preferably 8 to 13 g., per liter of copper as potassium copper cyanide or sodium copper cyanide 0.1 to 0.8 g. per liter of cadmium as potassium cadmium cyanide or sodium cadmium cyanide, and 3 to 8 g. per liter of free cyanide calculated as potassium cyanide.

Furthermore, the duration of the cathodic phase is 4 to seconds and the duration of the anodic phase 0.5 to 2 seconds and the current density during the cathodic phase is 0.5 to 1.5 a./dm. and the current density during the anodic phase is 0.75 to 3.75 a./dm. preferably 1.0 to 3.0 a./dm. The gold-copper-cadium alloys thus electrolytically deposited from cyanidic baths have such lustre that further polishing is unnecessary. On the other hand, when the gold alloy is deposited using current reversal techniques but operating outside of the limits indicated, the quality of the deposit is not improved over that obtained when operating without reversal of current but in most instances is of lower lustre.

The following examples will serve to illustrate the process according to the invention:

Example 1 An aqueous bath containing 2.2 g. per liter of gold as potassium gold cyanide, 12 g. per liter of copper as potassium copper cyanide, 0.5 g. per liter of cadmium as potassium cadmium cyanide and 7 g. per liter of free potassium cyanide was electrolysed with periodic reversal of current supplied to the electrodes. During the period of cathodic connection of the electrodes to the material to be gold plated, the current density was 1.5

a./dm. whereas during the period of the anodic connection the current density was 3.2 a./dm. The dura tion of the cathodic connections was 7.5 seconds each,

whereas the duration of the anodic connections was 1.2

3,056,733 Patented Oct. 2, 1962 seconds each. The procedure was continued until a gold alloy plate 20 thick had been attained.

Example 2 An aqueous bath containing 1 g. per liter of gold as potassium gold cyanide, 8 g. per liter of copper as potassium copper cyanide, 0.15 g. per liter of cadmium as potassium cadmium cyanide and 3.5 g. per liter of free potassium cyanide was electrolysed with periodic reversal of current supplied to the electrodes. During the period of cathodic connection of the electrodes to the material to be gold plated, the current density was 0.6 a./dm. whereas during the period of the anodic connection the current density was 1.0 a./dm.. The duration of the cathodic connections was 4 seconds each, whereas the duration of the anodic connections was 0.8 second each. The procedure was continued until a gold alloy plate 20;]. thick had been attained.

The gold alloys deposited according to the invention have the following properties: They are highly lustrous and require no further polishing. They are of high gold content and therefore resistant against tarnish. They are hard and resistant to abrasion. They also are of good colortone.

Their composition is 10 20% Cu, 10 20% Cd and the remainder gold, preferably, 12 13% Cu, 12 13% Cd and the remainder gold.

The high current densities employed produce a high plating speed so that the process is very economical.

The ratio of the current density during the cathodic phase to the current density during the anodic phase is less than 1:15, preferably 1:2.

I claim:

1. In a process for the electrolytic deposit of gold-cop per-cadmium alloys from aqueous alkaline cyanide baths using periodically reversed direct current, the steps which comprise electrolytically depositing a gold-copper-cadmium alloy from an aqueous cyanide bath maintained at a pH of 9 11 and containing 1 to 3 g. per liter of gold as potassium gold cyanide, 5 15 g. per liter of copper as an alkali metal copper cyanide selected from the group consisting of potassiumand sodium copper cyanides, 0.1 to 0.8 g. per liter of cadmium as an alkali metal cadmiurn cyanide selected from the group consisting of potassiumand sodium cadmium cyanides and 3 to 8 g. per liter of free cyanide calculated as potassium cyanide, the duration of each cathodic phase being 4 to 20 seconds and the duration of each anodic phase being 0.5 to 2 seconds and maintaining a current density of 0.5 to 1.5 a./dm. during the cathodic phase and a current density of 0.75 to 3.75 a./dm. during the anodic phase, whereby the ratio of cathodic to anodic current density is less than 1:1.5.

2. The process of claim 1 in which the current density employed during the anodic phase is 1.0 to 3.0 a./dm.

3. The process of claim 1 in which the bath contains 8 to 13 g. per liter of copper as alkali metal copper cyanide.

4. The process of claim 1 in which the gold alloy deposited is of the following composition 10 20% Cu, 10 20% Cd and the remainder Au.

5. The process of claim 1 in which the gold alloy deposited is of the following composition 12 13% Cu, 12 13% Cd and the remainder Au.

References Cited in the file of this patent UNITED STATES PATENTS 2,141,157 Peterson Dec. 20, 1938 2,451,341 Iernstedt Oct. 12, 1948 2,724,687 Spreter et a1 Nov. 22, 1955 FOREIGN PATENTS 1,032,636 Germany June 19, 1958 

1. IN A PROCESS FOR THE ELEECTROLYTIC DEPOSIT OF GOLD-COPPER-CADMIUM ALLOYS FROM AQUEOUS ALKALINE CYANIDE BATHS USING PERIODICALLY REVERSED DIRECT CURRENT, THE STEPS WHICH COMPRISE ELECTROLYTICALLY DEPOSITING A GOLD-COPPER-CADMIUM ALLOY FROM AN AQUEOUS CYANIDE BATH MAINTAINED AT A PH OF 9 - 11 AND CONTAINING 1 TO 3 G. PER LITER OF GOLD AS POTASSIUM GOLD CYANIDE, 5-15 G. PER LITER OF COPPER AS AN ALKALI METAL COPPER CYANIDE SELECTED FROM THE GROUP CONSISTING OF POTASSIUM- AND SODIUM COPPER CYANIDES, 0.1 TO 0.8 G. PER LITER OF CADMIUM AS AN ALKALI METAL CADMIUM CYANIDE SELECTED FROM THE GROUP CONSISTING OF POTASSIUM- AND SODIUM CADMIUM CYANIDES AND 3 TO 8 G. PER LITER OF FREE CYANIDE CALCULATED AS POTASSIUM CYANIDE, THE DURATION OF EACH CATHODIC PHASE BEING 4 TO 20 SECONDS AND THE DURATION OF EACH ANODIC PHASE BEING 0.5 TO 2 SECONDS AND MAINTAINING A CURRENT DENSITY OF 0.5 TO 2 A./DM.2 DURING THE CATHODIC PHASE AND A CURRENT DENSITY OF 0.75 TO 3.75 A./DM.2 DURING THE ANODIC PHASE, WHEREBY THE RATIO OF CATHODIC TO ANODIC CURRENT DENSITY IS LESS THAN 1:1.5. 